Goethite (FeO(OH)),
(pronounced: "Gertite") named after the German
polymath Johann Wolfgang von Goethe, is an
iron bearing oxide mineral found in soil and other low-temperature
environments. Goethite has been well known since prehistoric
times for its use as a
pigment.
Evidence has been
found of its use in paint pigment samples taken from the caves of Lascaux
in France
.
It was
first described in 1806 for occurrences in the Mesabi iron ore district of Minnesota
.Recently, nanoparticulate
authigenic goethite was shown to be the most
common
diagenetic iron oxyhydroxide in
both marine and lake sediments.
Composition
It is an
iron
oxyhydroxide. Goethite's hardness ranges from 5.0 to 5.5 on the
Mohs Scale, and its
specific gravity varies from 3.3 to
4.3. The mineral forms prismatic needle-like
crystals, but is more typically massive.
Feroxyhyte and
Lepidocrocite are both polymorphs of the iron
oxyhydroxide FeO(OH). Although they have the same chemical formula
as goethite they each have different crystalline structures making
them distinct minerals.
Usage
Its main modern use is as an
iron ore,
being referred to as
brown iron ore. It does have some use
as a
clay earth pigment. Iron
rich
lateritic soils developed over
serpentinite rocks in tropical climates
are mined for their iron content as well as other metals.
Formation
Goethite often forms through the
weathering of other iron-rich minerals, and thus
is a common component of
soils. It may also be
precipitated by
groundwater or in other
sedimentary conditions, or form as a primary mineral in
hydrothermal deposits.
Prevalence
Goethite is found all over the planet, usually in the form of
concretions,
stalactitic formations,
oolites (a form consisting of tiny round grains
cemented together), reniform (kidney shapes) or botryoidal
(globular, like bunches of grapes) accumulations. It is frequently
encountered in the swampy areas at the head of spring waters
('
bog iron'), on cave floors, and on the
bottom of lakes and small creeks. The
boxworks or
gossan resulting from the
oxidation of sulfide ore deposits is formed of
goethite along with other iron oxides and quartz.
Significant deposits of goethite are found in
England
, Australia, Cuba
, and
Michigan
, Minnesota, Missouri
, Colorado
, Alabama
, Georgia
, Virginia
, and Tennessee
in the United States
.
Deposits
significant in location, if not in abundance, have been found in
Gusev
by NASA's Spirit rover,
providing strong evidence for the presence of liquid water on the
planet Mars in an earlier stage of its
development.
References
See also
Wikis
Quiz
Map
Search